Motor vehicle wheel alignment systems are important for ensuring that the alignments of wheels are within the specifications provided by motor vehicle manufacturers. If wheels are out of alignment, there may be excessive or uneven tire wear. In addition, the performance of the vehicle, particularly handling and stability, may be adversely affected if the wheels are not properly aligned. As used herein, "wheel" refers to the tire and wheel assembly found on a motor vehicle. Such an assembly is generally comprised of a conventional tire that is mounted on a metal wheel or "rim."
The wheels of a motor vehicle may be aligned in a number of ways. For example, an operator or an alignment technician can use a vision imaging apparatus such as a machine vision system that employs optical sensing devices, such as cameras, to determine the positions of various objects. An example of such machine vision systems is the apparatus and method described in U.S. Pat. No. 5,809,658, entitled "Method and Apparatus For Calibrating Cameras Used in the Alignment of Motor Vehicle Wheels," U.S. Pat. No. 5,724,743, entitled "Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels," and U.S. Pat. No. 5,535,522, entitled "Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels." The apparatus described in these references is sometimes called a "3D aligner" or simply an "aligner." FIG. 1 provides a top view schematic of such an aligner. The aligner of FIG. 1 is discussed in more detail below.
The alignment of wheels of a motor vehicle may be affected by changes in the size of the wheels. Even small changes in the size of the wheels can cause large changes in the alignment. As a result, most automotive manufacturers recommend that the alignment technician inspect all wheels to ensure that they are matched (e.g., that they are all the same size), that the tires on the wheels are not worn, and that each tire is properly inflated. If any of these problems exist, the alignment technician should correct them before continuing with the alignment. Unfortunately, the alignment technician may forget to perform such inspections and repairs, or the alignment technician may have difficulty assessing the condition of the tires. In either case, the alignment may be adversely affected, potentially resulting in degraded performance of the vehicle.
In addition, the alignment specifications provided by the automotive manufacturers are referenced to the plane that the vehicle is sitting on, also known as the "gravity plane" or the "rack plane." However, in some alignment systems, such as the aligner noted above, the alignment measurements that are taken are referenced to the plane passing through the center of the wheels, also known as the "vehicle plane." For vehicles with the same size wheels, the rack plane and vehicle plane are parallel. But if the wheels have different sizes, the rack plane and the vehicle plane are not parallel. As a result, the manufacturer specifications cannot be compared directly to the alignment measurements taken by the aligner.
The alignment technician must also have relevant information readily available to properly perform the alignment. Such information may include: the size of the wheels; the relative size of the wheels in comparison to one another; the automotive manufacturer specifications; the measured wheel alignments; and the results of adjusting either the measured wheel alignments or the manufacturer specifications for the angle between the rack plane and the vehicle plane when using alignment systems such as the aligner noted above.
Based on the foregoing, there is a clear need in this field for an apparatus and method that provides measurements indicating the size of the wheels of a motor vehicle.
There is also a need for an apparatus and method that determines if there are differences between the sizes of the wheels of a given motor vehicle.
There is also a need for an apparatus and method that displays the results of wheel measurements to aid an alignment technician with the following tasks: detecting wheels with low air pressure; determining if some wheels have more wear than others; identifying if the wheels on a vehicle are mismatched; or indicating that there is unequal suspension loading.
There is also a need for an apparatus and method that measure the angle between the rack plane and the vehicle plane so that a technician may determine if these planes are parallel.
There is also a need for an apparatus and method that can adjust the measured alignments to achieve correct alignment if the rack plane and the vehicle plane are not parallel.
It would be advantageous to have an apparatus and method that, as part of the alignment process, automatically determines and displays important information, such as the following: the sizes of the wheels; comparisons among the wheels of a motor vehicle; the alignment specifications of the automotive manufacturer; the measured alignments; and the results of adjusting either the measured wheel alignments for the angle between the rack plane and the vehicle plane.